drm/i915: Move number of scalers initialization to runtime init

In future patches, we require greater flexibility in describing
the number of scalers available on each CRTC. To ease that transition
we move the current assignment to intel_device_info.

Scaler structure initialisation is done if scaler is available on the CRTC.
Gen9 check is not required as on depending upon numbers of scalers we
initialize scalers or return without doing anything in skl_init_scalers.

v3: Changed skl_init_scaler to intel_crtc_init_scalers

v2: Added Chris's comments.

Signed-off-by: Nabendu Maiti <nabendu.bikash.maiti@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v2)
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1480398794-22741-1-git-send-email-nabendu.bikash.maiti@intel.com